This utility patent application claims priority to German Patent Application No. 100 38 114.6, filed Aug. 4, 2000.
1. Field of the Invention
The present invention relates to a method and a device for conditioning comminuted tobacco material by heating and moistening with water vapor.
The term xe2x80x9ccomminuted tobacco materialxe2x80x9d is here to be understood, for example, as threshed tobacco leaf, tobacco stems, tobacco stalks, each of these cut or comminuted, recycled tobacco as well as tobacco by-products such as tobacco primary winnowings and tobacco secondary winnowings.
Such methods are mainly used for pre-conditioning comminuted tobacco material, as the first stage of an expansion method, in order to increase the so-called xe2x80x9cfilling capacityxe2x80x9d of the tobacco material.
Freshly harvested, green tobacco leaves contain relatively high proportions of water, which is reduced to a residual water content of less than 10% by means of various methods described as xe2x80x9ccuring methodsxe2x80x9d. The raw tobacco prepared in this way is taken to factories for the manufacture of, for example, cigarettes or other luxury food.
The processing chain from greenleaf to raw tobacco, however, causes a considerable shrinkage of the tobacco material, and this reduction in volume has a disadvantageous effect on the filling capacity.
Various methods have therefore been developed to at least partly reverse this reduction in volume, exploiting the fact that the cell framework of comminuted tobacco material can comprise the volume originally found in the leaf.
Amongst known expansion processes, two groups of cases are distinguished, namely: the High Order Process, wherein the tobacco is loaded into an autoclave with a slightly volatile propellant, such as for example carbon dioxide or nitrogen, whereby increases in the filling capacity in the range of 100%, compared with the measuring value after cutting, may be achieved if the method is suitably carried out; or the Low Order Process, wherein the pre-conditioning with water vapor is followed by drying, for example in an flow dryer, a fluid or vortex dryer or a drum dryer. Drying is followed by so-called post-conditioning, comprising re-moistening, sieving and cooling. Using low order processes, the filling capacity may be increased by up to 50%.
The present invention concerns a low order expansion process, wherein the tobacco material is pre-conditioned by being pre-heated/pre-moistened with water vapor and then dried.
2. Review of the Prior Art
Various low order expansion processes are already known. DE 37 10 677 C2 shows an expansion device comprising a cellular wheel sluice for feeding the tobacco material to an expansion chamber formed by a sub-domain of the cellular wheel sluice. A hot gas consisting of air and water vapor is introduced into the expansion chamber, such that the tobacco material is accelerated by a pressure drop to at least 50 m/s, the tobacco material remaining in the expansion chamber less than 0.1 s.
WO 99/23898 describes a device for saucing and moistening tobacco. Tobacco is introduced into the device by an airlock, in such a way that no air can enter the device. The tobacco falls downward through the device and is sprayed with vapor/water/casing and other materials by side nozzles. The pressure of the nozzles is in the range 0.1 to 10 bars. The treatment takes place at atmospheric pressure, since no lock to the treatment area is provided on the discharge side.
WO 97/04673 discloses a method for expanding tobacco stems, pressurized in a locked container by means of saturated vapor, until all the cells of the stems are moistened. Then the pressure is quickly reduced, whereby the cells xe2x80x9cexplodexe2x80x9d. Due to its discontinuous batch-wise function this system is not economically optimal.
Finally, a method and device of the cited type follow from DE 197 34 364 A, wherein comminuted tobacco material is introduced into a chamber via a cellular wheel sluice. In this chamber, the tobacco material free-falls downward, radially through a rotating jet curtain of the conditioning medium. In addition, a conveying means, specifically a Winnover cylinder, is arranged inside the chamber, rotating about an axis running substantially perpendicular to the flow direction of the tobacco, and comprises substantially radially extending nozzles openings for the conditioning medium.
Said Winnover cylinder also serves to disperse the tobacco consisting of more or less clumped together strands.
An additional cellular wheel sluice may be provided on the discharge side (see FIG. 4), transporting the tobacco to an oscillating conveyor to be transported on to a drying means.
A disadvantage of this type of pre-conditioning is the mechanical demands on the tobacco in order to disperse the clumps, which are caused by the fats which melt on the surface of the tobacco particles during heating and moistening.
It is the underlying object of the invention to provide a method and a device for (pre-) conditioning comminuted tobacco particles, wherein the aforementioned disadvantages do not arise. In particular, a method and a device are to be suggested which make no mechanical demands on the delicate tobacco particles while retaining the advantages of a continuous operation method.
The present invention proposes a method for condition comminuted tobacco material by heating and moistening with water vapor, wherein:
a) said comminuted tobacco material free-falls down through a chamber operating in a continuous process; and
b) is treated during said free-fall with water vapor via nozzles, wherein
a hyperbaric pressure is maintained in said chamber.
Furthermore, the present invention proposes a device for conditioning comminuted tobacco material by heating and moistening with water vapor, comprising:
a) a chamber in which said comminuted tobacco material free-falls downwards;
b) a cellular wheel sluice at each of the upper inlet and the lower outlet of said chamber; and
c) nozzles for treating said free-falling, comminuted tobacco material with water vapor;
wherein:
d) both cellular wheel sluices are formed as pressure differential proof sluices,
such that a hyperbaric pressure of more than 1 bar is maintained in said chamber.
Suitable embodiments are defined by the accompanying sub-claims.
The advantages achieved by the invention are based on the following considerations: an increase in the filling capacity, measured in comparison with the filling capacity value after the tobacco has been cut, can be affected by increasing the moistness with which the pre-conditioned tobacco enters the dryer, the so-called dryer entry moistness. At given dryer parameters, in particular given dryer geometry, and here again fixed dryer length, the filling capacity rises when the dryer entry moistness is increased.
Moreover, increasing the temperature of the tobacco at entry into the dryer has a positive effect on the filling capacity, as this leads to a fast exchange of energy/heat and material between the gas phase in the dryer and the tobacco particles, which is in turn highly important for successful drying with respect to the filling capacity.
The invention achieves this additional improvement in the exchange of energy/heat and material through (pre-)conditioning under pressure, i.e. conditioning at an absolute pressure of more than 1 bar. In addition, the flow of tobacco, continuously falling downward, is treated with vapor in a chamber which is formed to be pressure differential proof, in such a way that a temperature and a pressure are set in the chamber in accordance with the vapor pressure line of the saturated vapor.
It is also possible in this respect to feed superheated vapor into the chamber and thus to achieve temperatures in the chamber above the corresponding equilibrium pressure.
With such pre-treatment, tobacco may be pre-heated to 180xc2x0 C., if a pressure of 10 bars absolute is maintained in the interior of the chamber. Pre-heating is here combined with simultaneous moistening. Since this process is initiated by condensing, temperature and moistness are quickly set to equilibrium conditions.
The tobacco, pre-conditioned under pressure, is taken directly, without intermediate storage, from the pre-conditioning chamber into the hot air stream of the dryer, forcing the tobacco to assume the corresponding equilibrium temperature of the water, in dependence on the pressure and temperature prevailing in the dryer. This means that by exploiting the thermal energy stored in the tobacco, vaporization takes place with cooling down to the so-called cooling limit temperature, which at ambient pressure lies between about 40xc2x0 C. and 98xc2x0 C., depending on the vapor content and the temperature of the atmosphere in the dryer. If a dryer is used at higher pressures, higher cooling boundary or limit temperatures may also be achieved.
It is thus possible to devise vaporization processes based on the presence of thermodynamic imbalances, without convectional exchange of heat, i.e. the exchange of energy between the drying gas and the tobacco particles in systems with forced movement.
This type of demoistening in the dryer is distinguished by its extremely high vaporization rates, and results in an additional gain in filling capacity as compared with conditioning in open, atmospheric systems, such as e.g. a drum or steam tunnel.
In a preferred embodiment, the water vapor is fed into the chamber through ring nozzles arranged flush with the inner surface area of the chamber, to rule out catching edges which could impede the passing of the tobacco.
Although the discharge direction of the nozzles may in principle be directed horizontal or even upwards, against the flow of tobacco, the discharge direction of the nozzle in accordance with a preferred embodiment is inclined downwards, to assist the conveying/flight movement of the tobacco, thus accelerating free-fall and ultimately increasing the rate of the method.
The vapor may be fed into the chamber at any desired angle, even for instance tangentially. However, it preferably runs at an angle of 90xc2x0 to the circumferential direction of the chamber wall, in order to achieve as high an impact effect as possible.
To avoid water vapor condensing on the inside wall of the pressure container, the container should be provided with a heating jacket, into which vapor of a slightly higher temperature than the vapor temperature of the (ring) nozzle vapor temperature is likewise fed.
The chamber should expand downwardly in a sort of tapered manner, since any risk of an occlusion can then be ruled out as far as possible.
Care should be taken that the tobacco falls through the chamber without building up, since build upxe2x80x94otherwise often used to generate a resting timexe2x80x94is not necessary in this type of processing, because the equilibrium temperature is set very quickly by the condensation.
In order to avoid any unwanted build-up of tobacco in the pressurized chamber, the discharge sluice should be run at a slightly higher conveying volume than the feed sluice. This may be achieved, for example, via the speed of the sluice and/or a greater chamber volume for the sluice chamber.
Once it has passed through the pressurized chamber, the pre-heated and moistened, i.e. pre-conditioned, tobacco is fed into a dryer, for which known conventional dryers, such as for example drum dryers or fluid bed dryers, may be used. The filling capacity is not, however, raised by the more slowly proceeding drying in these variants to the same extent as when an airflow dryer is used, which is thus preferred.
The pre-conditioned tobacco discharging from the lower cellular wheel sluice is thus swept along by the hot gas stream of said airflow dryer, and dried to its desired discharge moistness by its resting time in this dryer section.
Said drying of the tobacco is characterized in the first stage by the quick vaporization, up until the cooling limit or boundary temperature is reached; in this way, the vaporization energy is exclusively provided by the tobacco particles themselves.
In the second section, by contrast, the tobacco is dried by convectional exchange of material and heat. This second drying process is slower than vaporization, and thus contributes proportionally less to increasing the filling capacity.
Even if the less favorable embodiments of dryers, namely drum dryers or fluid bed dryers, are used, higher filling capacities are achieved by the vaporization and drying processes described above than by the conventional combination of a pre-heating drum/steam tunnel with a drum/fluid bed dryer.
As already indicated above, the use of a cellular wheel sluice which is xe2x80x9cpressure differential proofxe2x80x9d is important, that is to say a cellular wheel sluice which, despite unavoidable leakage due to sealing problems on the one hand, and vapor leaking out via the individual chambers of the cellular wheel sluice on the other hand, maintains a largely constant absolute pressure in the chamber interior, and therefore a constant pressure differential between the atmospheric pressure outside the chamber and the interior pressure of the chamber. Suitable cellular wheel sluices which are pressure differential proof are available on the market.